Field of the Invention
The present invention provides a method of producing a polyolefin composition comprising contacting a binuclear metallocene pre-catalyst and a co-catalyst, adding a excess of a metal alkyl, then adding a first olefin monomer. The method allows for the production of polyolefins with a highly stereoregular stereochemical microstructure through living coordination polymerization in which rapid reversible chain transfer between a racemic mixture of a chiral active transition metal propagating center and multiple equivalents of inert main group metal alkyl is competitive with chain-growth propagation at the active center. By virtue of the slower rate of chain-transfer relative to propagation that can be achieved with a binuclear catalyst relative to the corresponding mononuclear catalyst, the present invention provides a work-around solution to the intrinsic limitation on product volume imposed by a traditional living polymerization, as well as a work-around solution to the stereochemically random microstructure that is normally obtained as the result of rapid and reversible chain-transfer between two populations of chiral active propagating centers, of opposite absolute configuration, when a racemic mixture of the pre-catalyst is employed. In essence, the field of invention is defined as stereoselective living coordinative chain-transfer polymerization.
Related Art
Several transition-metal-based catalysts have been reported that can mediate the living metal-mediated coordination polymerization (also known as homogeneous, single-site Ziegler-Natta polymerization) of ethene, propene, higher α-olefins, and α,ω-nonconjugated dienes, and, in some cases, these proceed with a high degree of stereocontrol (tacticity) ((for a review of catalysts for living coordination polymerization of ethene and α-olefins, sec: Coates, G. W., et al., Angew. Chem. Int. Ed. 41:2236-2257 (2002)); (for the living and stereoselective coordination polymerization of α-olefins and α,ω-non-conjugated dienes, see: Jayaratne, K. C., et al., J. Am. Chem. Soc. 122:958-959 (2000); Jayaratne, K. C., et al., J. Am. Chem. Soc. 122:10490-10491 (2000); Keaton, R. J., et al., J. Am. Chem. Soc. 123:6197-6198 (2001); Zhang, Y., et al., Chem. Commun. 2358-2359 (2003); Zhang, Y., et al., Organometallics 23:3512-3520 (2004); Harney, M. B., et al., Angew. Chem. Int. Ed. 45:2400-2404 (2006); Harney, M. R, et. al., Angew. Chem. Int. Ed. 45:6140-6144 (2006); Zhang, W., et al., Adv. Synth. Catal. 350:439-447 (2008))). However, the commercialization of new polyolefin materials and products that take advantage of the unique capabilities of living coordination polymerizations appears unlikely (for reviews of polyolefin materials prepared through living coordination polymerization, see: Domski, G. J., et al., Prog. Polym. Sci. 32:30-92 (2007); Sakuma, A., et al., Polym. J. 1 39:193-207 (2007); Szwarc, M., et al., Ionic Polymerization and Living Polymers; Chapman & Hall: New York (1993); Quirk, R. P., et al., Polym. Int. 27:359-367 (1992); Matyjaszewski, K., J. Phys. Org. Chem. 8:197-207 (1995)).
The same fundamental criterion of a living polymerization, namely, chain-growth propagation in the absence of irreversible chain termination, serves to establish a “one polymer chain per active metal center” cap on product yield as a critical liability. The severity of this liability sharply increases as the targeted number-average degree of polymerization, Xn, of the desired polyolefin product decreases. While living coordination polymerization is ideally suited for accessing the largely unexplored material science and technology associated with architecturally well-structured ‘precision polyolefins’ of very low to moderate molecular weights (ca 500-10,000 Da), the practical availability of significant quantities of these materials presently remains out of reach due to unfavorable weight (polymer) to weight (catalyst) ratios ((for a review of catalysts for living coordination polymerization of ethene and α-olefins. See Coates, G. W., et al., Angew. Chem. Int. Ed. 41:2236-2257 (2002)); (for reviews of polyolefin materials prepared through living coordination polymerization, see Domski, J., et al., Prog. Polym. Sci. 32:30-92 (2007); Sakuma, A., et al., Polym. J. 39:193-207 (2007); Szwarc, M., et al., Ionic Polymerization and Living Polymers; Chapman & Hall: New York (1993); Quirk, R. P., et al., Polym. Int. 27:359-367 (1992); Matyjaszewski, K., J. Phys. Org. Chem. 8:197-207 (1995); Kaneyoshi, H., et al., Macromolecules 38:5425-5435 (2005); Ring, J. O., et al., Macromol. Chem. Phys. 208:896-902 (2007); Ventolá, L., et al., J. Phys. Chem. Solids 66:1668-1674 (2005))).
U.S. Pat. No. 8,188,200 discloses the living coordinative chain-transfer polymerization and copolymerization of ethene, propene, long-chain α-olefins, and α,ω-nonconjugated dienes using {η5-C5Me5)Hf(Me)[N(Et)C(Me)N(Et)]}[B(C6F5)4] as the active transition-metal initiator for chain-growth propagation with multiple stoichiometric equivalents of diethylzinc (ZnEt2) as surrogate chain growth sites. Successful living coordinative chain-transfer polymerization of these monomers requires that the rate, and rate constant for reversible (polymeryl group) chain transfer between the active transition-metal propagating centers, and the inactive surrogate main-group metal species, vct and kct, respectively, should be far greater than the corresponding kinetic parameters for transition-metal-mediated propagation, vp and kp, in order to insure that all active and surrogate species appear to propagate at the same rate.
To address the problems inherent with the ‘one catalyst-one material’ strategy, several strategies have been introduced to achieve ‘catalyst-many materials’ by using dynamic processes competitive to chain propagation. For example, Waymouth and Coates took advantage of conformational flexibility in unconstrained ‘oscillating’ metallocenes to prepare atactic-isotactic stereoblock polypropenes such as elastomers and softened theromoplastics. See Coates, G. W., et al., Science 267:217-219 (1995) and Lin, S., et al., Acc. Chem. Res. 35:765-773 (2002). However, no method has been developed to directly modulate chain propagation rates in a single catalyst system.
It is well-known that co-catalyst and the resulting anion play an important role in homogeneous Zeigler-Natta polymerization by stabilizing the cationic transition metal center which is the initiator of olefin polymerization. See Kaminsky, W., et al., Adv. Polym. Sci. 127:144-187 (1997); Bohmann, M., J. Chem. Soc., Dalton Trans.:255-270 (1996); Brintzinger, H.-H., et al., Angew. Chem. Int. Ed. 34:1143-1170 (1995); Guram, A. S., et al., Comprehensive Organometallic Chemistry II, Chapter 2; Elsevier: Oxford (1995); Soga, K., et al., Catalyst Design for Tailor-Made Polyolefins; Elsevier: Tokyo (1994); Möhring, P. C., et al., J. Organomet. Chem. 479:1-29 (1994); Marks, T. J., Acc. Chem. Res. 25:57-65 (1992). Marks and co-workers reported that for olefin copolymerization, tris(2,2′,2″-nonafluorobiphenyl) borane (PBB) and tetrakis borate anion B(C6H5)4− derived cationic complexes exhibited higher catalytic activity and comonomer incorporation level than the MeB(C6H5)4− analogues. See Chen, Y.-X., et al., J. Am. Chem. Soc. 120:6287-6305 (1998); Chen, M. C., et al., J. Am. Chem. Soc. 123:11803-11804 (2001); Li, L., et al., J. Am. Chem. Soc. 124:12725-12741 (2002). MeB(C6H5)4− is a more coordinating anion than bulkier MePBB− and B(C6H5)4−, and the relatively stronger cation-anion ion pairing stabilizes highly electron-deficient metal centers. Higher hexene incorporation in copolymerization of ethene was observed by Waymouth and co-workers using methylaluminoxane (MMAO) instead of borane catalysts (Reybuck, S. E., et al., Macromolecules 38:2552-2558 (2005)). Therefore, the same transition metal pre-catalyst activated by different co-catalysts may show different polymerization characteristics, and having weak ion pairing after activation will yield high propagation rates and high comonomer incorporation level.
There is a need, for a method that produces of isotactic stereoblock polyolefin. Additionally, there is a need for a method that can be used to modulate the different grades of isotactic stereoblock polyolefin materials of varying average block length.